The present invention generally relates to pressure bladders, and more particularly, relates to transparent pressure bladders for welding plastics and the like materials utilizing electromagnetic radiation.
Welding is commonly used to join plastic or resinous parts, such as automobile thermoplastic parts, at a welding zone. Typically, lasers have been used to provide the heat necessary to perform this welding operation (for example, see U.S. Pat. No. 4,636,609, the disclosure of which is incorporated herein by reference). Such lasers provide a focused beam of electromagnetic radiation at a specified frequency (i.e., coherent monochromatic radiation).
Infrared lamps and heaters, among others, are also used to provide infrared radiation for heating a welding zone. One such process is Through-Transmission Infrared (TTIR) welding. The TTIR welding technique utilizes infrared radiation that passes through at least one part (sometimes called the xe2x80x9ctransmission piecexe2x80x9d) in order to heat the welding zone in at least one other part so as to provide sufficient heat to create a welded joint between the contacted parts.
As is common in many welding industries, undesirable results may occur as a result of improper contact between the parts being welded. That is, each of the parts being welded includes various inconsistencies or tolerances, which may effect the proper contact pressure between the parts in the area of the welding zone. The effect of failing to maintain proper contact pressure between the parts being welded in the area of the welding zone is a reduction in the integrity of the resultant welded joint. Accordingly, there is a need in the relevant art to provide a method of maintaining proper contact pressure between parts being welded to promote a strong and integral welded bond therebetween.
An ancillary concern when welding plastic or resinous parts is to also minimize undesirable effects, including deformation and marking of the overall part, caused by undesirable frequencies of radiation energy being passed into the parts being welded. Infrared lamps and heaters emit polychromatic radiation which typically has a broader frequency range (i.e., polychromatic) than laser sources. However, some of the frequencies within this broader range produce undesirable results. These undesirable frequencies heat portions of the parts beyond the targeted or desired welding zone and/or temperature, thereby possibly creating deformation and marking of the overall part. Solid materials have been used to selectively filter or absorb these undesirable frequencies before the radiation reaches the targeted parts. However, solid filters suffer from several disadvantages, including uncontrolled buildup of heat, as well as having to be continually replaced due to the damage or degradation caused by the radiation or heat byproduct. The degradation of the solid filter over a period of time inhibits the performance of the solid filter to absorb these undesirable wavelengths.
Accordingly, there exists a need in the relevant art to provide a method and apparatus capable of exerting a generally uniform pressure upon a part being welded to maintain proper contact pressure during the welding process to maximize the integrity of the welded joint. Additionally, there exists a need in the relevant art to provide a method and apparatus that is generally transparent to desired wavelengths of radiation, yet is generally opaque to undesirable wavelengths of radiation.
In accordance with the broad teachings of the present invention, a primary object of the present invention includes providing an improved pressure bladder for exerting generally uniform pressure upon the parts being welded to assure proper contact therebetween during the welding process. It is another object of the present invention to provide a pressure bladder that is generally transparent so as not to substantially limit the transmission of desired laser radiation to the welding zone. It is yet another object of the present invention to provide a generally transparent pressure bladder that may also act as a filter medium to substantially limit the undesirable radiation wavelengths, if needed. Lastly, it is an object of the present invention to provide a method and apparatus that will overcome the disadvantages of the prior art.
In accordance with the broad teachings of this invention, an inflatable bladder system for applying generally uniform pressure to parts being welded to insure proper contact at the welding interface having an advantageous construction and method of use is provided. The inflatable bladder includes a first sheet that is generally transparent to predetermined electromagnetic radiation to allow such radiation to pass therethrough. This electromagnetic radiation serves to heat the parts to a temperature sufficient to create a welded joint. The inflatable bladder also includes a second sheet that is also generally transparent to predetermined electromagnetic radiation to allow such radiation to pass therethrough. The second sheet is coupled to the first sheet to create a sealed volume therebetween. Fluid is selectively introduced into the sealed volume in order to expand the bladder into engagement with the parts being welded to exert a generally uniform pressure thereon.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only.